In a preferred embodiment the invention relates to a huge electrical machine, which is totally enclosed by a shell or housing.
Electrical machines needs cooling to dissipate heat, which is generated during its operation by an ohmic resistance, by iron hysteresis, etc.
It is possible to cool a small electrical machine by a heat-transfer from the inside of the machine to its surface.
This is not possible for a large machine, which shows a relatively small surface per power rating and heat generation.
When a machine is installed indoor at a dry atmosphere it is possible to operate the machine without a housing, so a cooling is achieved by the circulation of ambient air through the machine.
But when the machine is installed under harsh conditions, like it is for generators being used in offshore wind-turbines, the electrical machine need to be totally enclosed, so ambient air is not allowed to circulate through the machine. For this application dedicated cooling-systems are required.